Petrochemical refineries practice numerous processes for steam cracking or pyrolysis of hydrocarbons, such as ethane, propane, and heavier feed stocks, such as naphtha and the like, to produce ethylene and propylene. In these processes, an aromatic-rich concentrate is often produced as a by-product in such processes. In addition, plants are engaged in the processing of coal in order to produce light oils which are also rich in valuable aromatics.
In all these processes, however, it is necessary to provide a feedstock in which gum precursors such as dienes and pseudodienes have been substantially removed or converted to useful materials before such feedstocks can be employed in these aromatic extraction or processing units. The present invention provides a method by which aromatic-rich concentrates which heretofore were not susceptible to use as feedstocks in these processes, may be processed in order to remove gum precursors and place these aromatic concentrates in condition for use as feedstocks in aromatic extraction processes to produce the useful products described, as well as other processes.
It is known in the art to upgrade such by-product hydrocarbon mixtures, such as depentanized aromatic concentrate (DAC), heavy aromatic concentrate (HAC), dripolene, light oil, pyrolysis gasoline, light oil from coal processing and the like, by converting the diolefins contained in these materials to monoolefins and, if aromatics extraction is the goal of the process, converting the monoolefins to saturates. The processing method commonly employed to remove these olefinic materials is selective catalytic hydrogenation.
Processing sequences revealed by Griffiths and Luntz of the M. W. Kellog Co., The Oil and Gas Journal, Feb. 19, 1968; the article by Hobson, "Modern Petroleum Technology--BP Selective Hydrogenation Process," in Applied Science, 1973; and the article by Brownstein, Petroleum Technology, "The Impact of the Energy Crisis," published by Petroleum Publishing Co., all outline two-stage catalytic hydrogenation processes to hydrotreat a variety of aromatic concentrate type materials. The first stage selectively hydrogenates the diolefins in these concentrates to monoolefins. The operating conditions of the first stage include temperatures low enough so that the diolefins are hydrogenated to monoolefins instead of polymerizing, which causes catalyst deactivation. The effluent from stage one, with prior desulfurization if necessary, is a suitable blending stock for the motor fuel pool. The monoolefins in this material contribute to its octane number.
If ultimate use of the hydrotreated product is to be as a feedstock for extraction of valuable aromatic compounds, such as benzene and toluene, further catalytic hydrogenation and desulfurization is necessary. This is accomplished in the second stage of the hydrogenation unit, which operates at higher temperatures, where monoolefins are converted to saturates and molecularly-bound sulfur is converted to H.sub.2 S. These higher temperatures would polymerize any diolefins present, thus fouling the catalyst and necessitating shutdown of the unit to regenerate or replace the catalyst. The effluent from the second stage of the hydrogenation unit can then be charged to a unit designed to extract the valuable aromatic components of these materials.
Also employed in current methods of upgrading aromatic concentrate type materials is distillation of the effluent from the first stage of the hydrogenation unit before charging to the second stage to give an aromatic concentrate, especially if final products are to be extracted aromatics. After complete saturation and desulfurization in the second stage, methods for purification of the aromatics such as solvent extraction, extractive distillation, etc. are employed.
The above-mentioned methods for removing dienes, olefins, and sulfur require a great deal of hydrogen. This requirement, coupled with reactor down time for catalyst maintenance (due to gum forming) and down time to remove gum from preheaters, determines the economics of upgrading aromatic concentrate materials using these processing methods, and, when compared with a method requiring little or no hydrogen and little maintenance down time, these economics are relatively disadvantageous.
It is also known in the prior art that sulfur can be reacted with olefins such as ethylene. Illustrative of this type of prior art are U.S. Pat. Nos. 2,039,979 and 2,135,747 to Duecker. Sulfur has also been modified with an olefinic hydrocarbon polymer derived from petroleum, as illustrated by U.S. Pat. No. 4,059,500 to Vroom. Other prior art has modified sulfur with styrene, styrene derivatives, or a cyclodiene such as dicyclopentadiene. Exemplary of this type of prior art is U.S. Pat. No. 3,459,717 to Signouret, U.S. Pat. No. 2,806,843 to Welsh, U.S. Pat. No. 3,823,019 to Dale et al., U.S. Pat. No. 3,887,504 to Woo, U.S. Pat. No. 3,997,355 to Santucci et al., U.S. Pat. No. 4,001,179 to Woo, U.S. Pat. No. 4,022,626 to McBee et al., U.S. Pat. No. 4,001,179 to Woo, U.S. Pat. No. 4,022,626 to McBee et al., U.S. Pat. No. 4,164,428 to Simic, the text at page 627 of Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd Edition, Vol. 17, and B. R. Currell et al., Chapter 1 in New Uses of Sulfur (J. R. West, ed.), Advances in Chemistry Series 140, American Chemical Society, Washington, D.C., pp 1-17 (1975). The McBee et al. patent shows the use of dicyclopentadiene and styrene in combination as a modifying composition for sulfur.
Other prior art showing sulfur in combination with styrene or dicyclopentadiene is exemplified by U.S. Pat. No. 3,231,546 to Bertozzi et al. and by U.S. Pat. No. 3,264,239 to Rosen et al.
In addition, several formulations of a modified sulfur product called Sulphlex have been developed by the Southwest Research Institute in order to replace or extend asphalt in highway construction. Illustrative of these formulations is Sulphlex 126, which contains 61 wt. % sulfur and 13 wt. % of each of dicyclopentadiene, vinyltoluene and a light cut of coal tar; Sulphlex 230, which contains 70 wt. % sulfur and 15 wt. % of each of dicyclopentadiene and dipentene; and Sulphlex 233, which contains 70 wt. % sulfur, 12 wt. % dicyclopentadiene, 10 wt. % dipentene and 8 wt. % vinyltoluene.
The present invention is directed to the use of sulfur to remove gum precursors from hydrocarbon feedstocks to make the feedstocks useful as starting materials in aromatics extraction, as suitable components in motor fuel blending, and in other applications.